Fatty acid alkyl esters find use in a number of industries, for example mining (as collectors), agriculture (as adjuvants) and energy (biodiesel). Fatty acid alkyl esters are typically prepared from feedstocks including vegetable oil, animal fat and used cooking oil by converting the constituent fatty acid triglycerides and any free fatty acids. Typically, the esters are short-chain esters such as methyl esters.
Conventional processes for producing fatty acid alkyl esters from triglyceride-based oils typically involve, in a first step, heating the oils at about 60-65° C. in the presence of sulfuric acid and a large excess of methanol in order to convert free fatty acids into methyl esters. A key requirement for this step is that the amount of water present is no more than 1%. Under these conditions minimal transesterification occurs. In a second step, transesterification of triglycerides into the corresponding methyl esters employing sodium methoxide in methanol is performed. The second step is usually repeated in order to maximise conversion and yield.
The present inventors have surprisingly discovered that fat-containing feedstocks having a broad range of free fatty acid contents can be efficiently esterified and transesterified under aqueous conditions by use of selected sulfonated fatty acid derivatives as catalysts.